1. The Templars:
In Silithus kill Twilight Cultist people in their camps and collect a full set of Twilight Trappings ( https://classicdb.ch/item=52000 ), which consists of Mantle, Cowl and Robe! When you have a full set, go to one of the two Lesser Wind Stones around the Twilight Cultist camps. Put the Twilight set on and rightclick the Lesser Wind Stone.
Now you can spawn a random one of the four Templars (Azure Templar, Crimson Templar, Earthen Templar, Hoary Templar) and kill him. (He is soloable, but maybe you'll need to get one friend to kill him.
When you have killed the Templar, loot him and you will get an Abyssal Crest and maybe some green BoE item and if you're really lucky a blue BoP. Search for the name of each Templar on Anonymous or Anonymous to find out which one drops which BoP item. Bring the Abyssal Crest to Bor Wildmane in Cenarion Hold and you will get a Bag of Spoils ( Bag of Spoils content: https://classicdb.ch/item=52026 ) and 90 Silver. This quest is not repeatable.

2. The Dukes:
For the next steps you will need at least a Friendly reputation with the Cenarion Circle.
Get the Aurel Goldleaf quest from Huum Wildmane and go talk to Aurel Goldleaf. For the following quest you will need another 3 Abyssal Crests from Templars and 1 Large Brilliant Shard. Collect those 4 items and give them to Aurel Goldleaf. Now you will receive a Twilight Cultist Medallion of Station. You will need it and another set of Twilight Trappings to spawn one of the Dukes (Duke of Cynders, Duke of Fathoms, Duke of Shards, Duke of Zephyrs) at a Wind Stone (a normal one, not lesser, not greater). For these bosses you will need a good group of 5-7 people. The Dukes drop an Abyssal Signet, which you can give to Bor Wildmane to get 1.85 Gold and a Sack of Spoils ( https://classicdb.ch/item=52153 for content ). The Dukes also drop other nice stuff such as blue BoE pants and other blue items.

--Everything below this line is unconfirmed, since i haven't got that far yet--

3. The Bosses:
For the next steps you will need at least an Honored or Revered reputation with the Cenarion Circle.
Get the quest Goldleaf's Discovery from Huum Wildmane and go talk to Aurel Goldleaf. Then you will need another 3 Abyssal Signets from Dukes and 5 Large Brilliant Shards. Collect those items and give them to Aurel Goldleaf. Now you will receive a Twilight Cultist Ring of Lordship. You will need it plus a Twilight Trappings set plus a Twilight Cultist Medallion of Station to spawn one of the big bosses (Baron Kazum, High Marshal Whirlaxis, Lord Skwol, Prince Skaldrenox) at a Greater Wind Stone. For the big bosses you will need a group of 25-40 people. The bosses drop an Abyssal Scepter and epic stuff.&nbsp Again, give the Abyssal Scepter to Bor or Humm Wildmane to get a Chest of Spoils (content: https://classicdb.ch/item=52296 ) and 2.8 Gold.

How to get reputation with Cenarion Hold:
To get reputation farm Twilight Cultist guys and Templars and finish repeatable quests such as https://classicdb.ch/quest=8318 for which you will need Encrypted Twilight Texts which drop from Twilight Cultist mobs.

farmed 34 dukes today with the same group..
we had: 2 mages, 1 warrior, 1 rogue, 1 warlock, 1 druid and me (paladin), all lvl 60

its not fun to have to farm sets with ur group because it might take long. So my trick is to buy the sets on AH (2g for each piece) then get alot of crests, transform them into the medallions, and buy more sets. Each group member was able to summon 3 when we joined each other.

once u kill some, u get the hang of it.. dont worry!

we each took turns to summon, then warrior tanked, when the Duke was at 95% rogue joined fight, and the casters just did their thing while druid and me healed.
It worked well, until druid left and i waisted a set and medallion by summoning and dying..

do NOT summon if u are not 100% sure that u will succeed! its just waist of grinding hours..

after u have killed the duke, just move on to the next camp and kill the duke there.. with an epic mount it wont take long to travel..

Drops were awsome, they dropped a rare item 30/34 times.. even one epic.. rare drops were Darkstone Claymore, Abyssal Pants (sells for 120-180g) and some others..

There are different types of Dukes..
The easiest is Duke of Shards (huge golem, only has one AoE attack that stuns u)
Second is Duke of Cynders (Lucifron wannabee with a fire AoE attack)
Third is Duke of Fathoms (a hydra that hits hard)
Hardest is Duke of Zephyrs! (flying serpent, with a very nasty lightning AoE attack.. nearly everyone wiped because of his AoE!)

loot rules were: everyone pass on signet exept the summoner, greed on BoE (need if u need) and pass/roll if need or FFA on BoP.. those rules worked very well, and we only had a few problems because someone rolled need instead of greed..

Grind with guildies! its not fun if u need a thing and it gets ninjaed by a stranger!

if u have a good group like i had, its more fun than MC!

This now gives 350 reputation. Also you get 25 rep for killing one of the dukes.

Process is as follows:

STEP 1:
Obtain 4 sets of Twilight Trappings http://classicdb.ch/?itemset=492 (head, shoulders, and chest) by killing the any of the humanoids at the twilight camps. Drop rate on each piece is 4%, so on average you will get one set every 25 kills. That's "on average", so expect to have lucky streaks and unlucky streaks.

STEP 2:
Wear a set of Twilight Trappings. Click on a LESSER WIND STONE. A dialogue box opens with only one option. Before you click on it, equip you normal head, shoulder, and chest gear as you will soon be fighting. Click on the dialogue option. In a couple secconds, a flash of lighning will strike you (does no damage) and one set of Twilight Trappings will disapear from your inventory. A Templar will appear at the stone. For about 5 seconds it will just sit there and can't be attacked yet. Then it goes aggressive on the person who did the summoning. Kill the Templar, and loot the Abyssal Crest.

STEP 3:
Repeat step 2, and then repeat it again. You should now have 3 Abyssal Crests, and you should still have one set of Twilight Trappings.

STEP 4:
You will now need 1 Large Brilliant Shard, and you must be friendly with Cenarion Circle to continue.
Do the "Aurel Goldleaf" quest from Huum Wildmane if you haven't done it already. Complete that quest by talking to Aurel Goldleaf. For the follow on quest, give her the 3 Abyssal Crests and the Large Brilliant Shard, for which she will give you 1 Twilight Cultist Medallion of Station.

STEP 5:
Go back to one of the Twilight camps and find a WIND STONE (not a "lesser" and not a "greater"). Clear the area around the stone. Put on a set of Twilight Trappings and also put on the Twilight Cultist Medallion of Station. Click on the Wind Stone. You will see a dialogue box, just like in step 2. Switch back into your normal gear. Click on the dialogue option. One set of Twilight Trappings and the Twilight Cultist Medallion of Station will disapear from your inventory, and one of the 4 DUKEs will be summoned. As before, there is a 5 second pause before the Duke will go agro. Kill the duke and loot the Abyssal Signet. Note, if you fail to kill the Duke, or it evades for any reason, it will despawn and you have to start all over from step 1. You do not get any of the materials refunded to you.

STEP 6:
Go back to Bor Wildmane and turn in the Abyssal Signet for your reward.

REPEATING FOR MORE TURN INS:
You can turn in more Abyssal Signets to get more rewards, but each turn in after the first requires 3 Abyssal Signets. You have to repeat steps 1 - 5 for each Abyssal Signet, so that's 3 full repetitions to get another Sack of Spoils.

Is it worth it?
My first time doing this was solo as a 70 BM hunter. The randomly summoned duke was the Duke of Shards, who I downed with no trouble. The duke dropped Abyssal Plate Legplates of Restoration http://classicdb.ch/?item=20671
I turned in the quest, opened my Sack of Spoils and got Lord Alexander's Battle Axe http://classicdb.ch/?item=13003
From wowhead's loot tables:
Getting a BoE blue drop from a duke is about a 25% chance.
Getting a BoE blue drop from the Sack of Spoils is also about a 25% chance.
It can be a fairly time consuming process to go through and the odds of getting nothing are fairly high, so weigh the cost before you set out on this venture.